Adipose tissue macrophages have been proposed as a link between obesity and insulin resistance. However, the mechanisms underlying these processes are not completely defined. Calpains are calcium-dependent neutral cysteine proteases that modulate cellular function and have been implicated in various inflammatory diseases. To define whether activated calpains influence diet-induced obesity and adipose tissue macrophage accumulation, mice that were either wild type (WT) or overexpressing calpastatin (CAST Tg), the endogenous inhibitor of calpains were fed with high (60% kcal) fat diet for 16 weeks. CAST overexpression did not influence high fat diet-induced body weight and fat mass gain throughout the study. Calpain inhibition showed a transient improvement in glucose tolerance at 5 weeks of HFD whereas it lost this effect on glucose and insulin tolerance at 16 weeks HFD in obese mice. However, CAST overexpression significantly reduced adipocyte apoptosis, adipose tissue collagen and macrophage accumulation as detected by TUNEL, Picro Sirius and F4/80 immunostaining, respectively. CAST overexpression significantly attenuated obesity-induced inflammatory responses in adipose tissue. Furthermore, calpain inhibition suppressed macrophage migration to adipose tissue in vitro. The present study demonstrates a pivotal role for calpains in mediating HFD-induced adipose tissue remodeling by influencing multiple functions including apoptosis, fibrosis and inflammation.
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The study was supported by a Beginning Grant-in Aid (13BGIA14560001) and Scientist Development Grant (14SDG18740000) from the American Heart Association, a Pilot award from the DRC at Washington University (5P30DK020579), and by the National Institutes of Health (Grants P20GM103527, R01HL130086).
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-017-14719-9.
Muniappan, Latha; Javidan, Aida; Jiang, Weihua; Mohammadmoradi, Shayan; Moorleghen, Jessica J.; Katz, Wendy S.; Balakrishnan, Anju; Howatt, Deborah A.; and Subramanian, Venkateswaran, "Calpain Inhibition Attenuates Adipose Tissue Inflammation and Fibrosis in Diet-Induced Obese Mice" (2017). Saha Cardiovascular Research Center Faculty Publications. 34.